The present invention is directed to electrical shift control devices for bicycle transmissions and, more particularly, to a motion sensor for use with a bicycle sprocket assembly.
Motion sensors are commonly used with bicycles to sense rotation of the wheel or pedal crank so that bicycle speed and cadence may be computed by a bicycle computer and displayed to the rider. Such information also may be used to control an automatic or semiautomatic bicycle transmission, wherein the bicycle speed or cadence may be used to determine when to change gear ratios. The typical motion sensor usually comprises a magnet attached to the wheel or crank arm and a magnetic sensor attached to the bicycle frame. When the magnet passes in close proximity to the magnetic sensor, the sensor provides a pulse to the bicycle computer. The speed or cadence then may be computed based on the elapsed time between successive pulses.
A disadvantage of traditional motion sensors is that they increase the number of parts at various locations on the bicycle, thus giving the bicycle a cluttered appearance. Furthermore, the appearance of a magnet rotating with the spokes can be disconcerting. Also, as the number of electronically controlled components increases, the amount of wiring needed to connect the various components together also increases. For example, if the bicycle uses an electronically controlled transmission, then wires must be routed for the wheel magnetic sensor, the crank magnetic sensor, the front transmission and the rear transmission. The aesthetic appearance of the bicycle is greatly diminished by such excessive wiring.
The present invention is directed to a motion sensor for use with a bicycle sprocket assembly wherein a magnet or first sensor element is mounted for rotation with the sprocket assembly. Another feature of the present invention is a magnetic sensor or second sensor element being mounted in close proximity to the bicycle transmission. Associating the first sensor element with the sprocket assembly eliminates the requirement of mounting the first sensor element on the spokes, and mounting the second sensor element in close proximity to the bicycle transmission allows the wiring for the second sensor element, if any, to be combined with any wiring or cables already routed to the transmission. The present invention thus combines various structures and functions in proximity to each other and results in a less cluttered appearance for the bicycle.
In one embodiment of the present invention, a sensor retainer for a bicycle sprocket assembly includes an annular member for mounting and rotating coaxially with the bicycle sprocket assembly and a sensor element fixed to the annular member. Alternatively, the sensor retainer may include a fixing member for mounting a derailleur or other transmission to a bicycle frame and a sensor element mounted to the fixing member.
In a more specific embodiment, a sensor assembly for a bicycle includes a plurality of sprockets mounted together for rotation around a common axis; a first sensor element coupled for rotation with the plurality of sprockets; and a second sensor element for attachment in close proximity to the plurality of sprockets so that the first sensor element rotates relative to the second sensor element. If desired, the first sensor element may include a signal generating element such as a magnet, and the second sensor element may include a signal receiving element such as a magnetic sensor. The second sensor element may include a first sensor unit for communicating with the first sensor element and a second sensor unit for communicating with the first sensor element, wherein the first sensor unit is offset from the second sensor unit in a circumferential direction. Such a structure allows the direction of rotation as well as the speed of rotation of the plurality of sprockets to be determined.
In another embodiment of the present invention, the plurality of sprockets may include a first sprocket and a second sprocket, wherein the first sprocket includes a shift facilitating structure for facilitating shifting of a chain from the second sprocket to the first sprocket. In this embodiment the first sensor element may be located at a specified rotational position relative to the shift facilitating structure so that the position of the shift facilitating structure may be determined. This feature has special usefulness when the sensor assembly is used in conjunction with an electronically controlled derailleur because then the derailleur may be commanded to shift the chain from the second sprocket to the first sprocket when the shift facilitating structure is in the optimum rotational position.